The present invention relates to a multilayered wiring structure used in a hybrid integrated circuit or the like in which a plurality of integrated circuits are mounted, and a method of manufacturing the same.
In recent years, an increase in integration degree and operation speed of LSIs is remarkably high, and multi-pin chips that operate at a clock frequency of 100 MHz or more become commercially available. In a single chip-mounted package of such a high-speed chip, a delay in signal transmitted between the package and the printed circuit board is large, and the influence of parasitic capacitance or inductance of the package cannot be neglected in system design. Signal delay caused by the influence of the parasitic capacitance and inductance interferes with an increase in operation speed of the entire system.
In order to solve this signal delay, a technique is available with which chips are arranged as close as possible to each other to form a hybrid integrated circuit (multi-chip module: MCM). With the MCM, signal delay between chips caused by the package can be decreased, and the high operation speed of a single chip can be obtained even in a system composed of a plurality of chips.
FIG. 4 shows the arrangement of the MCM. The arrangement of the MCM will be described. A lower wiring layer 503 is formed on a die pad 501a on a lead frame 501 through an insulating layer 502, and an upper wiring layer 505 is formed on the lower wiring layer 503 through an interlevel insulating layer 504. An integrated circuit chip 506 and a resistor chip 507 are mounted at predetermined positions on the upper wiring layer 505. The integrated circuit chip 506 is connected to a predetermined portion of the upper wiring layer 505 with a wire 508. Predetermined portions of the upper wiring layer 505 and leads 501b are connected to each other with wires 508a. The resultant lead frame 501 is encapsulated with a molding resin 509 with the distal ends of the leads 501b being exposed.
The insulating layer 502 and interlevel insulating layer 504 described above are made of polyimide or the like, and the respective wiring layers are formed by patterning a conductor film formed on the insulating layer 502 and interlevel insulating layer 504 by vapor deposition or sputtering. The respective wiring layers are connected to each other through via holes 510.
The via holes 510 described above are roughly classified into two types, as shown in FIGS. 5A and 5B. The first type is called a stagger via hole type. According to this type, as shown in FIG. 5A, a via hole 603 to be connected to a lower wiring layer 601 is formed to continue to a wiring layer 604 through a hole (via hole) formed in an interlevel insulating layer 602 formed on the lower wiring layer 601. The stagger via hole is fabricated simultaneously with formation of the wiring material of the wiring layer 604.
The second type is called a filled via hole type, in which a filling layer is formed to fill a via hole. According to this type, as shown in FIG. 5B, a filling layer 603a is formed to fill a via hole formed in an interlevel insulating layer 602 formed on a lower wiring layer 601, and a wiring layer 604 is formed to be connected to the filling layer 603a. The filling layer 603a constituting this filled via hole is fabricated by, e.g., plating.
Since the stagger via hole is fabricated by a process such as vapor deposition or sputtering as described above, it is not suitable when forming via holes to overlap in the vertical direction. Due to this defect, the filled via hole formed by filling is superior.
Formation of a filled via hole will be briefly described. As shown in FIG. 6A, wiring layers 702 and 703 are formed on a substrate 701. As shown in FIG. 6B, an insulating layer 704 and a metal layer 705 respectively made of polyimide and a copper foil are formed to cover the wiring layers 702 and 703 on the substrate 701.
The resultant structure is processed by using a resist pattern as a mask, thus forming openings at predetermined regions of the metal layer 705. As shown in FIG. 6C, a metal pattern 705a is formed. The insulating layer 704 is etched by using the metal pattern 705a as a mask to form via holes 706 and 707. The resist pattern may be removed prior to formation of the via holes or during formation of the via holes simultaneously.
Copper is deposited on the wiring layers 702 and 703 exposed to the bottoms of the via holes 706 and 707 in accordance with electroplating using the wiring layers 702 and 703 as one electrode (cathode), to fill the via holes 706 and 707 with plated copper. When the surface of the copper portion growing by plating reaches the opening ends of the via holes 706 and 707, the upper end of the copper portion growing by plating comes in contact with the ends of the holes of the metal pattern 705a. When the copper portion growing by plating comes in contact with the metal pattern 705a, the metal pattern 705a becomes the common electrodeposition surface to grow copper. As shown in FIG. 6D, The via 706 and 707 are filled with filling layers 708 and 709, so that a copper plating film 710 is formed on the metal pattern 705a. 
When filling the via holes 706 and 707 with copper by electroplating, if the upper end of the copper portion growing by plating comes into contact with the ends of the holes of the metal pattern 705a, abnormal plating growth occurs at these contact portions. Accordingly, the copper plating film 710 forms projecting portions 710a at the ends of the holes of the metal pattern 705a. This leads to a nonuniformity in the surface, which is a problem. Therefore, the projecting portions 710a are removed by polishing or the like to planarize the surface of the copper plating film 710, as shown in FIG. 6E.
The metal pattern 705a and copper plating film 710 are processed and upper wiring layers 711 and 712 are formed, as shown in FIG. 6F. As a result, the wiring layers 702 and 703 are connected to the upper wiring layers 711 and 712 through the filling layers 708 and 709, respectively. The upper wiring layers 711 and 712 are continuous to the filling layers 708 and 709 as they are formed simultaneously with the filling layers 708 and 709 by copper plating growth. The connection state between the filling layers 708 and 709 and the upper wiring layers 711 and 712 is much more reliable than that obtained when the filling layers 708 and 709 and the upper wiring layers 711 and 712 are formed separately.
Conventionally, however, as described above, abnormal plating growth causes a projecting portion 710 (dog bone phenomenon). Polishing must be performed to planarize the projecting portion.
Generally, polishing requires a very large amount of know-how, and polishing itself decreases the yield. The higher the degree of micropatterning, the cleaner the atmosphere where formation of a multilayered wiring structure is performed must be. However, polishing is a major factor that degrades cleanliness.
In fine, conventionally, since polishing is required to form filling layers, the yield of the multilayered wiring structure is degraded. If filling layers and wiring layers are simply formed separately without using polishing, unevenness or the like occurs due to the dog bone phenomenon, and the filling layers and the wiring layer cannot be connected to each other reliably.
It is, therefore, a principal object of the present invention to improve the reliability in connection between the filling layer and wiring layer of a multilayered wiring structure without using a process such as polishing that decreases the yield.
In order to achieve the above object, according to the present invention, there is provided a multilayered wiring structure comprising a first wiring layer formed on a substrate through a first insulating layer, a second insulating layer formed on the first wiring layer to have a hole at a predetermined region thereof to expose an upper portion of the first wiring layer, a filling layer made of a conductive material to fill the hole, a second wiring layer formed on the second insulating layer to have an opening above a portion where the hole is formed, and a metal film formed on the second wiring layer to be connected to the filling layer.